Field of the Invention
The invention relates to a spark plug voltage probe in which a lead wire is provided through an insulation to electrically connect a high voltage induced by an ignition coil to a spark plug in an internal combustion engine, and detecting a voltage applied across the spark plug.
With the demand of purifying emission gas and enhancing fuel efficiency of internal combustion engines, it has been necessary to detect firing condition in each cylinder of the internal combustion engine. In order to detect the firing condition in each of the cylinders, an optical sensor has been installed within the cylinders on one hand. On the other hand, a piezoelectrical sensor has been attached to a seat pad of the spark plug.
In both cases, it is troublesome and time-consuming to install the sensor to each of the cylinders, thus increasing the installation cost, and at the same time, taking much time in check and maintenance.
Therefore, it is an object of the invention to provide a spark plug voltage probe which is capable of precisely detecting a voltage applied to the spark plug installed to each cylinder of the internal combustion engine with a relatively simple structure.